The present invention relates to surgical knives and particularly to knives used in ophthalmic surgery.
For many years, the predominant method of treating a diseased lens has been to remove the diseased lens and replace it with an intraocular lens ("IOL"). Two surgical procedures are preferred for removing the diseased lens: extracapsular cataract extraction and phacoemulsification. Extracapsular cataract extraction involves removing the lens in a relatively intact condition by use of a vectus or similar surgical instrument. Phacoemulsification involves contacting the lens with the vibrating cutting tip of an ultrasonically driven surgical handpiece to emulsify the lens, thereby allowing the emulsified lens to be aspirated from the eye. Although extracapsular cataract extraction has been the preferred surgical technique, phacoemulsification has become increasingly popular, in part because the cutting tip of the ultrasonic handpiece requires only a relatively small (approximately 3 to 3.5 millimeter) tunnel incision.
A typical posterior chamber IOL comprises an artificial lens ("optic") and at least one support member ("haptic") for positioning the IOL within the capsular bag. The optic may be formed from any of a number of different materials, including polymethylmethacrylate (PMMA), polycarbonate and acrylics, and it may be hard, relatively flexible or even fully deformable so that the IOL can be rolled or folded prior to insertion. The haptics generally are made from some resilient material, such as polypropylene or PMMA. IOL's may be characterized as either "one-piece" or "multi-piece." With one-piece IOL'S, the haptic and the optic are formed integrally as a blank and the IOL is then milled or lathed to the desired shape and configuration. Multi-piece IOL's are formed either by attaching the haptic to a preformed optic or by molding the optic around the proximal end of the haptic.
The diameter of the optic varies depending on the design of the IOL, but an optic diameter of around 5-6 millimeters (mm) is most common. Although some IOL's are made from a foldable material, allowing the IOL to be inserted through the typical 3 mm to 3.5 mm incision used with phacoemulsification, in general, the incision must be enlarged after the aspiration of the cataractous lens to allow the IOL to be implanted. Surgeons typically use a surgical knife with a blade width of approximately 3.2 mm for making the initial incision into the-anterior chamber and for widening the incision to approximately 5.2 mm for IOL insertion. While the knife must have a sharp point to make the initial incision, the sharp point is not needed to widen the incision, as an elongated or sharp point increases the possibility of damage to the iris or capsular bag. Therefore, the knife used to widen the initial incision preferably has a short, blunt nose.
Two prior art surgical knives sold for use as IOL implant knives have generally chevron-shaped blades, with blunt, V-shaped noses and parallel cutting sides. While the blunt noses reduce the risk of injury to the iris or capsular bag, the parallel sides increase the likelihood that the incision will be unnecessarily widened, particularly if there is any unintentional side-to-side movement of the knife while it is within the incision.
Accordingly, a need continues to exist for a surgical knife that will precisely cut the IOL implant incision used in phacoemulsification while at the same time, minimizing the likelihood of iris or capsular bag injury and unintentional widening of the incision.